Evaluating a leaf-level canopy assimilation model linked to CERES-Maize

The simple approach of calculating crop growth rate as the product of intercepted light and radiation use efficiency may not adequately represent plant growth under stress conditions. We developed a photosynthesis and respiration model for maize (Zea mays L.) and linked it to CERES-Maize v.3.7, calling the new model CERES-PR. The purpose of this work was to evaluate CERES-PR simulation of photosynthesis at three levels of integration: instantaneous leaf assimilation, hourly canopy assimilation, and seasonal crop growth under conditions where water and N supply were not limiting growth. Instantaneous leaf assimilation measured in field plots were obtained in the central portion of the 13th leaf on three dates during the grain filling to test the model at the leaf level. Carbon dioxide fluxes measured above the canopy with the eddy correlation technique were used to test the model at the canopy level. The progression of leaf area index (LAI) and aboveground biomass from experiments planted at latitudes ranging from 21 to 45 degrees N was used to evaluate the seasonal simulation of crop growth. CERES-PR was in close agreement with measured values. A sensitivity analysis indicated that the temperature function affecting leaf assimilation have a large impact in the simulated growth and grain yield. The new model provides opportunities to simulate plant processes more realistically under stress. Our future efforts will focus on developing new modules to simulate energy balance and stomatal conductance to incorporate into CERES-PR leaf-level C, water, and N balances.